1. Field of the Invention
The present invention relates to a flow control device and more particularly to a flow control device for controlling the flow rate of air passing through a by-pass air passage in an intake system of an internal combustion engine.
2. Description of the Prior Art
Heretofore, in flow control devices of this type there has been used a stepping motor 10 as an actuator, as shown in FIG. 1. With forward and reverse rotations of a rotor 16 of the motor 10, a shaft 80 reciprocates along the axis thereof.
A front end portion of the shaft 80 is positioned within a by-pass air passage 81, and a valve body 82 is provided on the shaft. The valve body 82 moves in contact with or away from a valve seat 83 provided in the passage 81 in accordance with a reciprocating motion of the shaft 80. With this movement of the valve body 82, the flow path area of the passage 81 increases or decreases to control the amount of air to be supplied.
In the case where two or more by-pass passages are required for the internal combustion engine and the flow rate of air in these by-pass passages are required to control synchronously, it is necessary to provide a plurality of flow control devices in such a number as the number of by-pass passages.
Furthermore, in the case where each of the flow control devices has different operative features with each other, the time necessary to actuate the valve body of each of the flow control devices after an electric signal is fed to the stepping motor differs with each other, resulting in that synchronous actuation of all the flow control devices is deteriorated.